Project Summary/Abstract Tobacco education campaigns are an effective tool for reducing youth tobacco use. The Food and Drug Administration (FDA) has invested heavily in its The Real Cost youth tobacco prevention campaign, spending $250 million on the campaign between 2013-2016 alone. Campaign evaluations have demonstrated that greater exposure to The Real Cost ads is associated with higher cigarette risk beliefs and lower smoking initiation among youth. A critical task that campaign designers must continually engage in, however, is the development and selection of ads that will most impact youth. In the current proposal, we argue The Real Cost campaign could achieve even greater impact if it had a rigorously validated, youth-targeted measure that could predict the impact of The Real Cost ads. Currently, the FDA uses a perceived message effectiveness (PME) scale to select ads for The Real Cost campaign. This scale has several major limitations, including: 1) it was developed with adult smokers; 2) it was developed before the advent of e-cigarettes and vaping; and 3) it assesses message PME, while a growing literature suggests that effects PME better predicts the impact of ads on intention and behavior change. Thus, the absence of a validated, youth-targeted PME measure for use in youth tobacco prevention campaigns is a major gap in regulatory science. The primary goal of the proposed project is to fill this gap by developing and validating an effects PME scale for adolescent tobacco prevention. Another goal of the project is to compare the performance of this new scale to the FDA?s current message PME scale in a rigorous validation experiment. We will accomplish these goals through 3 aims. In Aim 1, we will develop a youth effects PME scale for vetting cigarette and e-cigarette prevention ads. We develop and refine an item pool, cognitively test items with adolescents (N=48), and conduct a scale development study with a national sample of N=800 adolescents. In Aim 2, we will establish whether effects and message PME prospectively predict the impact of smoking prevention ads on intentions to smoke cigarettes. We randomize N=1,280 adolescents at-risk of cigarette smoking to 1 of 3 The Real Cost cigarette prevention ad conditions or to a control ad condition. Participants view a set of ads each week and complete a final assessment at week 3, and we examine whether PME predicts the impact of ads on intentions to smoke (primary outcome), risk beliefs about smoking and smoking behavior (secondary outcomes). In Aim 3, we will examine whether effects and message PME predict the impact of vaping prevention ads on intentions to vape. We randomize N=1,024 adolescents to either The Real Cost e-cigarette ad condition or to a control ad condition, and examine whether PME predicts the impact of e-cigarette ads on intentions to vape and risk beliefs. The proposed research is responsive to the FDA interest areas of Communication and Behavior in funding announcement RFA-OD-18-002. This work will help campaign designers select more effective ads, thereby increasing the impact of tobacco education campaigns targeted to youth.